The present invention relates generally to the field of radiation sensitive positive and negative photoresist compositions, such as compositions containing novolak resins or vinyl phenol resins as the film forming binder resin, together with a photosensitizer, such as an acid generator, which can be e.g., a naphthoquinone diazide or an onium salt sensitizing agent. It is well known in the art to produce positive photoresist formulations such as those described in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. These include alkali-soluble phenol-formaldehyde novolak resins together with light-sensitive materials, usually a substituted naphthoquinone diazide compound. The resins and sensitizers are dissolved in an organic solvent or mixture of solvents and are applied as a thin film or coating onto a substrate suitable for the particular application desired.
The film-forming component of these photoresist formulations (and the photoresist formation) upon being coated on a suitable substrate is initially insoluble in an alkaline aqueous solution. Upon exposure of selected areas of the coated substrate to a selected wavelength of actinic radiation, however, the photosensitive component undergoes a radiation induced structural transformation and thereby renders the exposed areas of the photoresist coating more soluble in an aqueous alkaline solution than the unexposed areas (for a positive photoresist). The relief pattern of the photoresist on the substrate produced by this method is useful for applications including use as an exposure mask or a pattern such as is employed in the manufacture of miniaturized integrated electronic components. In many industrial applications, particularly in the manufacture of miniaturized electronic components, a photoresist is required to provide a high degree of resolution for line and space widths on the order of one half to one-quarter micron (micrometer) or less.
The ability of a photoresist to reproduce these very small dimensions, on the order of one half micrometer or less, is extremely important in the production of large-scale integrated circuits on silicon chips and similar components. Circuit density on such a chip can only be increased, assuming photolithography techniques are utilized, by increasing the resolution capabilities of the resist to provide smaller and smaller lines and spaces. Negative photoresists, wherein the exposed areas of resist coating become insoluble and the unexposed areas are dissolved away by the developer, have been extensively used for this purpose by the semiconductor industry. However, positive photoresists generally have inherently higher resolution and have been widely utilized as replacements for many negative resists in the production of advanced microelectronic devices.
This invention relates to a composition useful for cleaning excess photoresist composition from the edge of the surface of a substrate coated with such a photoresist composition utilizing an edge bead remover (EBR), and thereby providing a substantially uniform film of the photoresist composition on the surface of the substrate. The present invention also relates to the cleaning method using such a composition for removing the excess of the photoresist composition film from the edge of the substrate surface, while simultaneously providing the photoresist film with a smooth edge. A solvent or mixture of solvents that will both efficiently and completely remove excess thick film photoresist (greater than 20-30 micrometers thick) from the edge of the surface of a substrate, to thereby provide a smooth edge and without damage or contamination thereof, is needed.
An EBR for thin photoresist films (less than about 20-30 micrometers thick) is almost always a good solvent for casting such thin films. However, an EBR for a thick film photoresist requires much more than just being a good solvent for the photoresist composition. Well known solvents for photoresists, such as cyclopentanone, propylene glycol methyl ether (PGME), propylene glycol methyl ether acetate (PGMEA), and mixtures of PGME and PGMEA are all good solvents for photoresists. However, they all have serious deficiencies when used as an EBR for such a thick film photoresist. The surface of wafers coated with a thick film photoresist, after using these EBR""s, generally have stringers and poor coating track cleaning is achieved. The present invention seeks to solve the aforementioned disadvantages. In addition, in using an EBR in the production of microelectronic devices such as computer chips, it is also very advantageous that such a thick film EBR has extremely good volatility and it should not be used as the casting solvent for the thick film photoresist.
It has been found that solvent mixtures comprising a di(C1-C3) alkyl carbonate such as dimethyl carbonate and diethyl carbonate, mixed with a compatible solvent such as cyclopentanone, provide very good EBR""s for thick film photoresists. Although such dialkyl carbonate solvent mixtures can also be used as EBR""s for thin film and moderately thick photoresist films, they find particular applicability for use with thick films having a film thickness greater than about 20-30 micrometers.
The present invention provides a method of treating a photoresist composition film disposed on a surface which method comprises contacting said photoresist composition with a solvent mixture, in an amount sufficient to produce a substantially uniform film thickness of said photoresist composition across said surface, wherein said solvent mixture comprises from about 50 to about 80 parts by weight, based on the weight of the solvent mixture, of at least one di(C1-C3)alkyl (dimethyl, diethyl, dipropyl) carbonate and from about 20 to about 50 parts by weight, based on the weight of the solvent mixture, of cyclopentanone. The dialkyl carbonate is preferably dimethyl carbonate and the ratio of dialkyl carbonate to cyclopentanone is preferably in the range of from about 80:20 to 50:50, more preferably from about 65:35 to 80:20, even more preferably from about 70:30 to 80:20, and most preferably about 75:25. The especially preferred method of the present invention further comprises rotating the surface having the photoresist composition film disposed thereon at a speed sufficient to thereby spread the photoresist composition film to the edge of the rotating surface, contacting the solvent mixture with the surface of the photoresist composition film solvent mixture while continuing to rotate said surface, and thereby providing a surface with the photoresist composition disposed as a film in having a substantially uniform thickness.
The present invention further provides an edge bead remover (EBR) for a photoresist composition disposed as a film on a surface, the EBR consisting essentially of a solvent mixture comprising from about 50 to about 80 parts by weight, based on the weight of the solvent mixture, of at least one di(C1-C3)alkyl carbonate and from about 20 to about 50 parts by weight, based on the weight of the solvent mixture, of cyclopentanone. The dialkyl carbonate is preferably dimethyl carbonate and the ratio of dialkyl carbonate to cyclopentanone is preferably in the range of from about 65:35 to 50:50, more preferably from about 65:25 to 80:20, and most preferably is about 75:25.
The following specific examples will provide detailed illustrations of the present invention. These examples are not intended, however, to limit the scope of the invention in any way and should not be construed as providing conditions, parameters or values that must be utilized to practice the present invention.